A conventional probe apparatus includes a loader chamber 1 and a prober chamber 2 which are arranged adjacent to each other as shown in, e.g., FIG. 3. The loader chamber 1 includes a cassette receiving part 30 for receiving a cassette 20 containing a plurality of semiconductor wafers W therein, a wafer transfer mechanism (not shown) for loading and unloading the wafers W into and from the cassette one by one, and a pre-alignment mechanism (not shown) for pre-aligning a wafer W while transferring the wafer W by the wafer transfer mechanism. The prober chamber 2 has a mounting table 3 which is movable in X, Y, Z and θ directions while mounting thereon a wafer W, a probe card 4 having probes 4A to be brought into electrical contact with electrode pads of some devices among all devices in the wafer W mounted on the mounting table 3, a fixing mechanism 5 for fixing the probe card 4 by using a card holder (not shown), and a connection ring 6 for electrically connecting the probe card 4 and a test head T.
The electrical characteristics of the devices are inspected by bringing the devices into electrical contact with a tester (not shown) via the probe card 4, the connection ring 6 and the test head T under the control of a control unit.
Further, in FIG. 3, reference numeral ‘7’ indicates an alignment mechanism for position-alignment of the wafer W and the probe card 4 in cooperation with the mounting table 3; reference numeral ‘7A’ and ‘7B’ represent an upper camera and a lower camera; and reference numeral ‘8’ indicates a head plate to which the fixing mechanism 5 of the probe card 4 is attached.
Further, as illustrated in FIG. 4 for example, in the case of using the probe card 4 which simultaneously inspects two devices arranged in the X direction with a single contact, the probe card 4 is brought into electrical contact with two devices at a first contact position P1 so that the inspection of first two devices D is performed and the mounting table 3 is moved to the left side of the X direction to perform the inspection of next two devices D. Accordingly, the mounting table 3 is index-fed by a distance of two devices D in the X direction as indicated by the arrow shown in FIG. 4 until the inspection of last two devices D in a first row is completed at a contact position P2.
Afterwards, the mounting table 3 is index-fed upward in the Y direction by a distance of a single device D and is moved to a position to perform the inspection of first two devices D in a second row, and then, the mounting table 3 is index-fed by a distance of two devices D in the X direction opposite to the direction in the first row until the inspection of devices D in the second row is completed.
In the same manner, the inspection is repeatedly performed on devices D of each row until electrical characteristics of all devices subjected to be inspected of the wafer W are inspected, thereby detecting, if any, a defective device D. After the inspection of one wafer W is completed, the inspected wafer W is replaced with a next wafer W and, then, an inspection of electrical characteristics of the new wafer W is performed in the same manner described above.
FIG. 4 shows how the wafer W is being inspected. A reference numeral ‘4A’ in FIG. 4 indicates devices which are being inspected. Besides, a solid line drawn inside the wafer W represents devices D subjected to be inspected.
If a percentage of defective devices D exceeds an allowable range as a result of the first inspection, the same inspection is repeated again on the wafer W in order to confirm the percentage of defective devices D. When the percentage of defective devices D is within the allowable range in the second inspection, the inspected wafer is replaced with a new wafer W, and the new wafer W is inspected.
However, in the first inspection, as indicated by shading shown in FIG. 4, inspection errors occur in specific devices in a regular pattern. In that case, even if the second inspection is performed in the same sequence as that of the first inspection, the same result may be obtained, and the number of defective devices D (the shaded devices shown in FIG. 4) is not reduced. If such devices are determined as defective products, the production yield deteriorates. Further, additional time is required for such re-examination, so that an operation efficiency of the tester is reduced.